After patch 3.0 everything is a bit shit. I found the best bet is with a prot warrior. AoE stun before they could do stuff then mass nuke. And hope you don't face the same team over and over. Since they'll just pop their shields and reflects at the start after the first time. And since thunderstorm is reflectable too. We simply got no chance currently in 5v5. I dropped 200 rating myself, losing 30 rating per game, won 3 rating twice though!

Anyhow, few more days and WotLK.

We'll have to wait and see how things pan out at level 80. Currently no one will give you any solid advice. Simply because such solid advice is unexistant.